diff --git a/pkg/metrics/providers/prometheus.go b/pkg/metrics/providers/prometheus.go
index 146022bb..f99131c7 100644
--- a/pkg/metrics/providers/prometheus.go
+++ b/pkg/metrics/providers/prometheus.go
@@ -15,6 +15,8 @@ import (
 	flaggerv1 "github.com/weaveworks/flagger/pkg/apis/flagger/v1beta1"
 )
 
+const prometheusOnlineQuery = "vector(1)"
+
 // PrometheusProvider executes promQL queries
 type PrometheusProvider struct {
 	timeout  time.Duration
@@ -132,41 +134,15 @@ func (p *PrometheusProvider) RunQuery(query string) (float64, error) {
 	return *value, nil
 }
 
-// IsOnline calls the Prometheus status endpoint and returns an error if the API is unreachable
+// IsOnline run simple Prometheus query and returns an error if the API is unreachable
 func (p *PrometheusProvider) IsOnline() (bool, error) {
-	u, err := url.Parse("./api/v1/status/flags")
+	value, err := p.RunQuery(prometheusOnlineQuery)
 	if err != nil {
-		return false, fmt.Errorf("url.Parse failed: %w", err)
-	}
-	u.Path = path.Join(p.url.Path, u.Path)
-
-	u = p.url.ResolveReference(u)
-
-	req, err := http.NewRequest("GET", u.String(), nil)
-	if err != nil {
-		return false, fmt.Errorf("http.NewRequest failed: %w", err)
+		return false, fmt.Errorf("running query failed: %w", err)
 	}
 
-	if p.username != "" && p.password != "" {
-		req.SetBasicAuth(p.username, p.password)
-	}
-
-	ctx, cancel := context.WithTimeout(req.Context(), p.timeout)
-	defer cancel()
-
-	r, err := http.DefaultClient.Do(req.WithContext(ctx))
-	if err != nil {
-		return false, fmt.Errorf("request failed: %w", err)
-	}
-	defer r.Body.Close()
-
-	b, err := ioutil.ReadAll(r.Body)
-	if err != nil {
-		return false, fmt.Errorf("error reading body: %w", err)
-	}
-
-	if 400 <= r.StatusCode {
-		return false, fmt.Errorf("error response: %s", string(b))
+	if value != float64(1) {
+		return false, fmt.Errorf("value is not 1 for query: %s", prometheusOnlineQuery)
 	}
 
 	return true, nil
diff --git a/pkg/metrics/providers/prometheus_test.go b/pkg/metrics/providers/prometheus_test.go
index b5cae79a..ac42130d 100644
--- a/pkg/metrics/providers/prometheus_test.go
+++ b/pkg/metrics/providers/prometheus_test.go
@@ -147,22 +147,61 @@ func TestPrometheusProvider_RunQueryWithBasicAuth(t *testing.T) {
 }
 
 func TestPrometheusProvider_IsOnline(t *testing.T) {
-	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusBadGateway)
-	}))
-	defer ts.Close()
+	t.Run("fail", func(t *testing.T) {
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusBadGateway)
+		}))
+		defer ts.Close()
 
-	clients := prometheusFake()
+		clients := prometheusFake()
 
-	template, err := clients.flaggerClient.FlaggerV1beta1().MetricTemplates("default").Get(context.TODO(), "prometheus", metav1.GetOptions{})
-	require.NoError(t, err)
-	template.Spec.Provider.Address = ts.URL
-	template.Spec.Provider.SecretRef = nil
+		template, err := clients.flaggerClient.FlaggerV1beta1().MetricTemplates("default").Get(context.TODO(), "prometheus", metav1.GetOptions{})
+		require.NoError(t, err)
+		template.Spec.Provider.Address = ts.URL
+		template.Spec.Provider.SecretRef = nil
 
-	prom, err := NewPrometheusProvider(template.Spec.Provider, nil)
-	require.NoError(t, err)
+		prom, err := NewPrometheusProvider(template.Spec.Provider, nil)
+		require.NoError(t, err)
 
-	ok, err := prom.IsOnline()
-	assert.Error(t, err, "Got no error wanted %v", http.StatusBadGateway)
-	assert.False(t, ok)
+		ok, err := prom.IsOnline()
+		assert.Error(t, err, "Got no error wanted %v", http.StatusBadGateway)
+		assert.False(t, ok)
+	})
+
+	t.Run("ok", func(t *testing.T) {
+		expected := `vector(1)`
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			promql := r.URL.Query()["query"][0]
+			assert.Equal(t, expected, promql)
+
+			if assert.Contains(t, r.Header, "Authorization") {
+
+			}
+			header, ok := r.Header["Authorization"]
+			if assert.True(t, ok, "Authorization header not found") {
+				assert.True(t, strings.Contains(header[0], "Basic"), "Basic authorization header not found")
+			}
+
+			json := `{"status":"success","data":{"resultType":"vector","result":[{"metric":{},"value":[1545905245.458,"1"]}]}}`
+			w.Write([]byte(json))
+		}))
+		defer ts.Close()
+
+		clients := prometheusFake()
+
+		template, err := clients.flaggerClient.FlaggerV1beta1().MetricTemplates("default").Get(context.TODO(), "prometheus", metav1.GetOptions{})
+		require.NoError(t, err)
+		template.Spec.Provider.Address = ts.URL
+
+		secret, err := clients.kubeClient.CoreV1().Secrets("default").Get(context.TODO(), "prometheus", metav1.GetOptions{})
+		require.NoError(t, err)
+
+		prom, err := NewPrometheusProvider(template.Spec.Provider, secret.Data)
+		require.NoError(t, err)
+
+		ok, err := prom.IsOnline()
+		require.NoError(t, err)
+
+		assert.Equal(t, true, ok)
+	})
 }